The present invention relates to a battery control IC (Integrated Circuit) and its control method.
Among the CPUs (Central Processing Units) installed in PCs (Personal Computers), there is a type of CPU that has a function of changing its operating frequency (hereinafter called “variable frequency function”) in order to keep a balance among the power consumption, the calculation performance, and the reliability (life span). A CPU having the variable frequency function lowers the clock frequency in the normal operation state, and thereby prevents the increase of the power consumption, and/or maintains the CPU at a low temperature and thereby prevents the deterioration in the reliability. On the other hand, when the resource request from the application(s) increases, the CPU having the variable frequency function raises the clock frequency and thereby increases the calculation performance. However, if the clock frequency is kept at a high frequency for a long time, the power consumption and the temperature of the CPU increase and thus the reliability deteriorates. Therefore, the period during which the clock frequency is kept at a high frequency is limited to a short period such as 10 ms.
Note that when a CPU having a variable frequency function is driven by electric power supplied from a battery pack (battery) in which a plurality of secondary battery cells are combined, the clock frequency in the high-speed operation state is determined based on the amount of the available power of that battery pack. (More specifically, how much the clock frequency in the high-speed operation state should be increased from that in the normal operation state is determined based on the amount of the available power.) Note that it has been required that a battery control semiconductor integrated circuit device (hereinafter referred to as “battery control IC”) that calculates the available power value of a battery pack should calculate the available power value of the battery pack immediately within the short period in which the high-speed operation is performed.
Incidentally, Japanese Unexamined Patent Application Publication No. 2010-34016 discloses an evaluation apparatus that measures a detection current value of a discharge overcurrent with high accuracy. Further, Japanese Unexamined Patent Application Publication No. 2003-79059 discloses a vehicle-mounted battery pack control apparatus that prevents over-charging/over-discharging and is capable of widening the available capacity range of the battery with a simple configuration and thereby reducing the size and weight of the apparatus. Further, Japanese Unexamined Patent Application Publication No. 2001-51029 discloses a rechargeable battery including an internal circuit, capable of externally outputting the remaining capacity of the battery according to the usage state of the battery and capable of improving the usage efficiency of the rechargeable battery.